JP2011214042A - Method for manufacturing hot-dip galvannealed steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot-dip galvannealed steel sheet which reduces the cohesion of the plating film to a tool and the like, also has adequate appearance and has improved adhesiveness of the plating film.SOLUTION: The method for manufacturing the plated steel sheet includes: a first step (a) of forming an oxide layer on a surface of a base steel sheet by heating the base steel sheet in a heating furnace; a second step (b) of reducing the oxide layer by heating the base steel sheet on which the oxide layer has been formed, in a reducing furnace; and a third step (e) of hot-dip-galvanizing the steel sheet and alloying the plating film, in this order. The first step includes heating the base steel sheet to 750-850°C in a period of 45-120 seconds under an atmosphere in which the amount of oxygen is controlled to 0.3 vol.% or less and the amount of water vapor is controlled to 10-30 vol.% in the heating furnace. The first step also includes a pre-heating step of heating the steel sheet to 450-600°C at a temperature-raising rate (X) of 7.5-28°C/second and a post-heating step of further heating the steel sheet to 750-850°C at a temperature-raising rate of 0.30X-0.80X.

Description

  The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet, and in particular, can suppress adhesion of plating to a tool or the like and has good appearance properties (specifically, prevention of unplating and alloying failure). In addition, the present invention relates to a technique for improving the adhesion between the base steel sheet and the galvannealed layer (hereinafter sometimes referred to as “plating adhesion”).

  For the purpose of reducing the weight of automobiles and home appliances, the demand for steel sheets excellent in strength, ductility, and workability is increasing rapidly. When Si or Mn is added to the steel sheet, ductility and workability can be improved without impairing the strength. Therefore, steel with positive addition of Si and Mn is used as a steel sheet satisfying such characteristics. In addition, since the steel sheet is also required to have corrosion resistance, the need for an alloyed hot-dip galvanized steel sheet (GA steel sheet) that imparts corrosion resistance to steel containing Si or Mn is increasing year by year (hereinafter referred to as “plated steel sheet”). Sometimes called).

  An alloyed hot-dip galvanized steel sheet is generally produced by the following method. First, after the slab is hot-rolled and cold-rolled, a thin steel plate (base material steel plate) that is heat-treated as necessary is prepared. The surface of the base material steel plate may be cleaned by degreasing and / or pickling in the pretreatment step. Next, after the oil on the surface of the base steel plate is burned and removed in the preheating furnace, recrystallization annealing is performed by heating in an annealing furnace in a non-oxidizing atmosphere or a reducing atmosphere. Thereafter, the steel sheet is cooled to a temperature suitable for plating in a non-oxidizing atmosphere or a reducing atmosphere, and a small amount of Al (about 0.1 to 0.2% by mass) is added without being exposed to the air. Immerse in the plating bath. Since the surface of the base steel sheet taken out from the hot dip galvanizing bath surface in the vertical direction is wet with molten zinc, the compressed air is blown perpendicularly to the steel sheet surface from the wiping nozzle to remove excess hot dip galvanizing, and then the alloy An alloyed hot-dip galvanized steel sheet is obtained by heat treatment in the furnace.

  However, Si and Mn are easily oxidizable elements and are easily concentrated on the steel sheet surface. That is, when a steel sheet containing an easily oxidizable element is heat-treated, these elements are selectively oxidized and concentrated on the steel sheet surface (the interface side between the steel sheet and the plating layer) to form an oxide (Si-Mn-O). Etc.). Since these oxides remarkably reduce wettability with molten zinc at the time of plating, problems such as non-plating and poor alloying occur and appearance properties deteriorate. Since these easily oxidizable elements are difficult to suppress concentration even in a non-oxidizing atmosphere or a reducing atmosphere, the Si and Mn-containing steel sheets are required to improve the problems caused by the oxides.

  Therefore, a so-called “oxidation-reduction method” is used in performing hot galvanizing alloying using a steel plate containing Si or Mn easily oxidizable elements. In this “oxidation-reduction method”, hot-rolled and cold-rolled steel sheets were subjected to oxidation in an oxidizing atmosphere and reduction in a reducing atmosphere, followed by a predetermined hot-dip galvanizing treatment. This is a method of performing an alloying process later. Specifically, first, by heating (oxidizing) an annealing furnace as an oxidizing atmosphere, Fe, Si, Mn, and other oxides of easily oxidizable elements (Fe—Si) are sequentially formed on the surface of the steel plate from the steel plate side. An inner oxide layer mainly composed of -Mn-O) and an outer oxide layer mainly composed of iron oxide (Fe-O) are formed (see FIG. 1A). Next, by heating (reducing) the reducing furnace as a reducing atmosphere, the iron oxide is reduced, and a reduced iron (Fe) layer having excellent plating wettability is formed on the surface layer (outside) of the steel sheet. (See FIG. 1 (b)). Next, after the plating process, an alloying process is performed.

  However, according to this “oxidation-reduction method”, oxides of easily oxidizable elements such as Si and Mn (Si—Mn—O) may be inappropriately concentrated at the interface between the plating layer and the steel sheet. As a result, when the plated steel sheet is subjected to stress during forming or the like, problems such as peeling of the alloyed hot-dip galvanized layer from the base steel sheet occur (interfacial plating peeling). Furthermore, there is a problem that the plating adheres to the tool or the like during the processing of the plated steel sheet, and a problem that the appearance properties deteriorate due to non-plating or plating unevenness.

  For example, when alloyed hot-dip galvanized steel sheets are used in final products such as automobiles, building materials, and home appliances, various forming processes are performed, but if the amount of plating adhesion to the tool increases during processing, the formability is poor. In addition to the above problem, it is known that the corrosion resistance is adversely affected, and in some cases, the peeling powder from the plating layer causes surface defects during press formation.

As a technique for solving such a problem, Patent Document 1 manufactures a hot dip galvanized steel sheet having a beautiful surface appearance without unplating and excellent plating adhesion when a high Si content steel sheet is used as a base material. Technology has been proposed. Specifically, in an atmosphere containing O ₂ ≧ 0.1% and H ₂ O ≧ 1%, heating is performed at a temperature of 400 to 750 ° C. (A-band heating), and then O ₂ <0.1% In an atmosphere containing H ₂ O ≧ 1%, heating at a temperature of 600 to 850 ° C. (B-band heating), and then in an atmosphere containing H ₂ = 1 to 50% and having a dew point of 0 ° C. or less, An oxidation-reduction method in which hot galvanizing treatment is performed after heating (C-band heating) is disclosed. However, as a result of studies by the present inventors, it has been found that the technique disclosed in Patent Document 1 may cause adhesion of plating or peeling powder from the plating layer.

JP 2007-291498 A

  The present invention has been made in view of the above circumstances, and its object is to reduce the adhesion of plating to a tool or the like, to improve the appearance properties and to improve the plating adhesion, and to alloyed molten zinc. It is providing the manufacturing method of a plated steel plate.

  The manufacturing method of the plated steel sheet of the present invention that has solved the above-mentioned problems is as follows: C: 0.04 to 0.20% (meaning mass%, hereinafter all the same regarding chemical components), Si: 0.1 to 3 0.0%, Mn: 0.1 to 3.0%, a method for producing an alloyed hot-dip galvanized steel sheet, in which an alloyed hot-dip galvanized layer is formed on the surface of the base steel sheet, A first step of heating a base steel plate satisfying the composition in a heating furnace to form an oxide layer on the surface of the base steel plate, a first step of heating the base steel plate on which the oxide layer has been formed in a reduction furnace to reduce the oxide layer A second step, a third step of alloying after hot dip galvanization, and in this order, the first step includes an oxygen amount in the heating furnace of 0.3% by volume or less, a water vapor amount In an atmosphere controlled to 10 to 30% by volume in 45 to 120 seconds. Heating to a temperature of 50 to 850 ° C., and the first step is a pre-heating step of heating to a temperature of 450 to 600 ° C. at a temperature rising rate (X) of 7.5 to 28 ° C./sec. And a post-heating step for further heating to a temperature of 750 to 850 ° C. at a temperature rising rate of 0.30X to 0.80X.

  In a preferred embodiment, the base steel sheet further includes Ni: 2% or less (not including 0%), Cu: 2% or less (not including 0%), Mo: 2% or less (not including 0%), And B: contains at least one selected from the group consisting of 0.01% or less (not including 0%).

  In a preferred embodiment, the base steel sheet further includes Cr: 2% or less (not including 0%), Nb: 1% or less (not including 0%), V: 1% or less (not including 0%), And W: at least one selected from the group consisting of 0.3% or less (not including 0%).

  In a preferred embodiment, the base steel sheet further contains Al: 0.06% or less (not including 0%) and / or Ti: 0.1% or less (not including 0%).

  In a preferred embodiment, the base steel sheet further contains at least one element selected from the group consisting of Ca, Mg, and REM: 0.03% or less (excluding 0%) in a total amount.

  In the present invention, the hot dip galvanizing treatment and the alloying treatment are carried out after the reduction after forming an oxide layer on the surface of the base steel sheet containing Si and Mn, which are easily oxidizable elements, under appropriate heating conditions. The amount of zinc contained in the plating layer can be controlled appropriately, and the distribution state of the alloy elements in the oxide-containing layer formed between the base steel sheet and the galvannealed coating layer can be controlled appropriately. As a result, the adhesion of plating to a tool or the like can be reduced, and the appearance properties and plating adhesion of the plated steel sheet can be improved.

FIG. 1 is a diagram schematically showing a manufacturing process of an alloyed hot-dip galvanized steel sheet. FIG. 2 is a diagram schematically showing the surface state after the oxidation treatment. FIG. 3 is a diagram showing an element mapping result by EPMA.

  The inventors have alloyed a base steel sheet containing an easily oxidizable element (specifically, a base steel sheet containing 0.1 to 3.0% of Si and 0.1 to 3.0% of Mn). The alloyed hot-dip galvanized steel sheet with a hot-dip galvanized layer reduces the adhesion of plating to tools, etc., and prevents the occurrence of non-plating and alloying defects, improving the appearance and In order to improve the adhesion of the plating layer to the steel plate, extensive studies have been made. As a result, (A) the adhesion of plating is affected by the amount of zinc contained in the plated layer of the plated steel sheet, (B) the amount of zinc contained in the plated layer, the appearance properties of the plated steel sheet, and the plating adhesion Is affected by the oxide layer formed on the base steel plate before being immersed in the hot dip galvanizing bath. (C) Since this oxide layer is formed in the oxidation treatment step, the heating conditions in the oxidation treatment step are particularly important. The present inventors have found that the adhesion of plating to a tool, appearance characteristics, and plating adhesion can be improved by appropriately controlling the above, and the present invention has been completed (hereinafter, these may be simply referred to as “plating characteristics”). is there).

  In the present specification, among the plating layers and steel plates constituting the plated steel plate, the steel plate is particularly referred to as a “base steel plate”. The “base steel plate” corresponds to the steel plate before plating after hot rolling and cold rolling in the manufacturing process of the plated steel plate. Hereinafter, for convenience of explanation, “base steel plate” may be simply abbreviated as “steel plate”.

  First, how the present invention was completed will be described.

[1] Adhesion of plating The present inventors performed oxidation, reduction, hot dip galvanizing, and alloying treatments to produce an alloyed hot dip galvanized steel sheet. The relationship between this oxide layer and the amount of zinc contained in the plating layer was examined.

  FIG. 1 shows the surface condition (before plating) after oxidation treatment, reduction treatment, hot-dip zinc immersion treatment, and alloying treatment when the above-mentioned “oxidation-reduction method” is applied to the base steel sheet. It is the figure which showed typically the state of the inside of a steel plate or the surface layer of a steel plate, and the state of the steel plate after plating, and the state of the vicinity of a plating layer interface, and FIG. It is the figure which showed the state schematically.

  First, as shown in FIGS. 1A and 2, when the base steel plate is heated in a heating furnace (oxidation treatment), an oxide layer is formed on the surface of the base steel plate. An oxide of Fe (Fe—O) is generated from the surface of the base steel plate toward the outside (plating layer side), and an oxide layer containing Fe, Si, and Mn (Fe—Si—) toward the inside (base steel plate side). Mn—O) is formed. The oxide layer formed by growing outward from the surface of the base steel sheet is generally called an “outer oxide layer”, and the oxide layer formed by growing inward is generally called an “inner oxide layer”.

  Next, when the base steel sheet on which the oxide layer is formed is heated and reduced in a reduction furnace (reduction treatment), as shown in FIG. 1 (b), the outer oxide layer (Fe-O) is reduced to pure iron. Although it becomes a layer (Fe), the oxide (Si-Mn-O or Si-O) in the inner oxide layer (Fe-Si-Mn-O) or the grain boundary oxide (Si-O) is not reduced. It remains as it is.

  When the inner oxide layer is peeled from the base steel plate before the plating treatment, a gap is formed between the peeled inner oxide layer and the base steel plate (FIG. 1 (c)). When the steel sheet is immersed in a hot dip galvanizing bath in this state, as shown in FIG. 1 (d), not only hot dip galvanizing adheres to the outermost surface, but also hot dip galvanizing penetrates into this gap.

  When alloying is performed in such a state, as shown in FIG. 1 (e), not only an alloyed plating layer (Fe—Zn alloy) is formed on the outermost surface, but also molten zinc that has entered the gap portion. Since plating is also alloyed, it has been found that the amount of zinc per unit volume in the gap is excessive.

  As a result of performing element mapping analysis by EPMA on the portion where the inventors have excessive zinc content, as shown in FIG. 3, the inner oxide layer-derived layer is between the alloy layer and the base material (base steel plate). It was confirmed that a Si / Mn enriched layer enriched with Si or Mn was present in a wavy state. On the other hand, such a Si / Mn concentrated layer was not formed in the part where the amount of zinc was normal.

  Then, the adhesion property of the plating of the normal zinc content portion and the excessive zinc content portion was examined. In the normal zinc content portion, the adhesion of the plating to the tool did not occur during processing. On the other hand, in the excessive zinc amount portion, adhesion of plating to the tool occurred during processing.

  Based on these findings, the present inventors consider that if the peeling of the inner oxide layer and the outer oxide layer that occurs before plating can be prevented, excessive zinc content can be suppressed, and the oxidation formed in the oxidation step The properties of the layers were studied repeatedly. As a result, if the Si concentration contained in the inner oxide layer is increased, the adhesion between the base steel plate and the inner oxide layer is improved, and the base steel plate and the inner steel plate as shown in FIG. It has been found that an excessive amount of zinc can be eliminated because it is possible to prevent separation from the oxidization layer.

That is, when the concentration of Si contained in the inner oxide layer is increased, a complex oxide of Si and Fe (firelight: Fe ₂ SiO ₄ ) is densely formed on the surface of the base steel sheet, and this dense firelight is formed on the base steel sheet. It is considered that the adhesion between the base steel sheet and the inner oxide layer is improved in order to improve the consistency of the crystal grains of the inner oxide layer and the inner oxide layer.

  And, as a result of the study by the present inventors, in order to increase the Si concentration and effectively exert the effect of improving the adhesion between the base steel plate and the inner oxide layer by firelight, it is possible to control the oxidation conditions of the base steel plate. I found it important.

That is, when forming an oxide layer on the surface of the base steel sheet by oxidizing the base steel sheet, if the base steel sheet is exposed to a low temperature region for a long time in the initial stage of heating, it is not a firelight but mainly hematite (Fe ₂ 0 ₃ ) An oxide is formed. When an oxide layer containing a large amount of hematite is formed, the outward diffusion of Fe from the base steel sheet and the inward diffusion of oxygen from the atmosphere are hindered, so that the growth rate of the oxide layer is significantly delayed. Firelight is generated in a high temperature range, but once an oxide layer containing a lot of hematite is formed on the surface of the base steel plate, the formation of firelite is suppressed even if the heating temperature is increased. It has been found that the adhesion between the inner oxide layer and the inner oxide layer cannot be sufficiently increased.

[2] Appearance properties When the relationship between the oxide layer and the appearance properties of the plated steel sheet was examined, it was found that the appearance properties of the plated steel sheet were affected by the thickness of the outer oxide layer in the oxide layer. That is, when the outer oxide layer becomes thinner, the Fe layer (reduced layer) formed by reducing the outer oxide layer in the reducing furnace becomes thinner, so that the wettability with hot dip galvanizing becomes worse, and non-plating is not caused. It tends to occur. Further, when the outer oxide layer becomes thinner, the amount of Fe contained in the plating layer becomes insufficient, and thus a tendency to cause alloying failure when alloying is observed. Therefore, in order to improve the appearance properties of the plated steel sheet, it is considered that the outer oxide layer should not be thinned. On the other hand, if the outer oxide layer is made too thick, the Fe layer formed by reduction in the reduction furnace becomes too thick, so a hot dip galvanized layer is formed on this surface, and when this is alloyed, the Fe layer becomes the plated layer. As a result, the same problem as in the case where the plating layer becomes too thick and the amount of zinc is excessive occurs. Therefore, as a result of repeated investigations to suppress the excessive zinc content, the inventors of the present invention have good appearance properties, and as a result, by appropriately controlling the oxygen amount and the water vapor amount in the heating furnace, the outer oxide layer is desired. It was found that the thickness can be adjusted.

[3] Plating layer peeling On the other hand, when the plating adhesion was examined, when the plating layer was stressed, the stress was concentrated at the interface between the base steel sheet and the plating layer, and the phenomenon of peeling from this interface (interfacial plating) Peeling) is observed when a Si-added steel sheet containing at least Si is used as the base steel sheet, and it has been found that even when powdering does not occur, interfacial plating peeling may occur. .

  Therefore, the present inventors have further studied in order to prevent plating peeling at the interface when a Si-added steel plate is used as the base steel plate. As a result, it has been found that if the thickness of the inner oxide layer is reduced, the plating peeling at the interface can be prevented.

The inner oxide layer remains in the form of an oxide at the interface between the base steel plate and the plating layer even after heating in a reduction furnace or after forming a hot dip galvanized layer or an alloyed hot dip galvanized layer. Therefore, when Si-added steel sheet is used as the base steel sheet, the amount of Si contained in the inner oxide layer increases, so that a large amount of Si oxide such as SiO ₂ and Fe ₂ SiO ₄ remains at the interface between the base steel sheet and the plating layer. To do. Since such Si oxides are more fragile than oxides of other elements, it has been found that when stress is applied, the stress tends to concentrate on the Si oxide, and as a result, the plating layer peels from the base steel sheet. Therefore, as a result of repeated studies to improve plating adhesion, the present inventors have found that if the amount of Si contained in the inner oxide layer is not excessively increased, the peeling of the plating at the interface can be prevented.

  Based on this knowledge, the influence of the amount of oxygen in the heating furnace, the amount of water vapor, the heating temperature, and the heating time on the amount of Si contained in the inner oxide layer was investigated. As a result, the amount of Si contained in the inner oxide layer increases according to the amount of Si contained in the base steel plate, the amount of Si contained in the inner oxide layer increases as the heating time increases, and the heating temperature It was found that the amount of Si contained in the inner oxide layer increases as the value increases.

[4] Coexistence of appearance properties and plating adhesion As described above, to improve the appearance properties of the plated steel sheet, it is necessary to thicken the outer oxide layer, but if the outer oxide layer is made too thick, powdering will occur. Will occur. Moreover, in order to prevent plating peeling at the interface and improve plating adhesion, it is necessary to suppress the amount of Si contained in the inner oxide layer. However, since the amount of Si contained in the inner oxide layer increases as the inner oxide layer becomes thicker, it is necessary to reduce the thickness of the inner oxide layer in order to suppress the amount of Si contained in the inner oxide layer. However, the thicknesses of the outer oxide layer and the inner oxide layer are correlated, and when one thickness is increased, the other thickness also increases. Therefore, in order to improve both appearance properties and plating adhesion, it is necessary to increase the thickness of the outer oxide layer relative to the thickness of the entire oxide layer and to reduce the thickness of the inner oxide layer.

  Therefore, in the present invention, studies have been made with the aim of thinning only the inner oxide layer. As a result, it has been clarified that the thickness of the inner oxide layer is greatly affected by the amount of oxygen contained in the atmosphere when heated to a high temperature. That is, as the amount of oxygen contained in the atmosphere in the heating furnace heated to a temperature of about 550 to 700 ° C. increases, the thicknesses of the outer oxide layer and the inner oxide layer both increase. However, the amount of increase in the thickness of the inner oxide layer with respect to the amount of increase in the oxygen amount is smaller than the amount of increase in the thickness of the outer oxide layer with respect to the amount of increase in oxygen amount. It was found that the thickness of the inner oxide layer relative to the thickness of the entire oxide layer can be reduced.

[5] Coexistence of plating adhesion and plating adhesion To suppress plating adhesion as described above, it is necessary to increase the Si concentration contained in the inner oxide layer, but the Si concentration is excessively increased. As a result, the plating adhesion deteriorates. Therefore, in the present invention, in order to suppress the adhesion of plating, it is not necessary to simply increase the Si concentration, but based on the knowledge that it is necessary to form the firelight densely as described above, The heating conditions were examined. As a result, in order to suppress the formation of hematite and promote the production of firelight, it is important to control the temperature rise rate in the heating furnace. It has been found that a two-stage temperature increase pattern in which the temperature increase rate at the latter stage of heating is slower than the temperature increase rate at the previous stage of heating may be adopted. It has been found that by adopting such a temperature rising rate, adhesion of plating can be secured while suppressing adhesion of plating.

  As mentioned above, based on the knowledge of [1]-[5], the manufacturing method of the galvannealed steel plate based on this invention derived | led-out is C: 0.04-0.20%, Si: 0.1-3 0.0%, Mn: 0.1 to 3.0%, the manufacturing method of the galvannealed steel sheet in which the galvannealed steel alloy layer is formed on the surface of the base steel sheet has the above chemical composition composition. A first step of heating a satisfactory base steel plate in a heating furnace to form an oxide layer on the surface of the base steel plate; a second step of heating the base steel plate on which the oxide layer has been formed in a reduction furnace to reduce the oxide layer A process, a third process of alloying after hot dip galvanization, and in this order, the first process has an oxygen content in the heating furnace of 0.3% by volume or less and a water vapor content of 10%. In the atmosphere controlled to -30 volume%, the said base steel plate is 750-850 degreeC in 45-120 second. And the first step includes a pre-heating step of heating to a temperature of 450 to 600 ° C. at a temperature rising rate (X) of 7.5 to 28 ° C./second, and 0.30X And a heating post-stage step of further heating to a temperature of 750 to 850 ° C. at a temperature rising rate of ˜0.80X.

  The reason why such a range is specified will be described below.

  First, the component composition of the base steel sheet used in the production method of the present invention will be described.

  The base steel sheet contains C: 0.04 to 0.20%, Si: 0.1 to 3.0%, and Mn: 0.1 to 3.0%.

C: 0.04 to 0.20%
C is an element necessary for improving the strength of the steel sheet, and in order to exert such an effect, 0.04% or more is contained. A preferable amount of C is 0.05% or more, more preferably 0.06% or more. However, if C is added excessively, the cold workability deteriorates, so the content is made 0.20% or less. A preferable amount of C is 0.15% or less, more preferably 0.12% or less.

Si: 0.1-3.0%
Si is an element useful for increasing the strength without deteriorating ductility and workability, and is contained in an amount of 0.1% or more in order to effectively exhibit such action. Since Si is an easily oxidizable element, conventionally, when Si is contained in an amount of 0.1% or more, there has been a problem that appearance properties and plating adhesion deteriorate. In contrast, in the present invention, since the oxide layer is formed by appropriately controlling the atmosphere and heating conditions in the heating furnace, Si is added to the oxide-containing layer formed between the base steel plate and the plating layer. Even if Si is contained in the base steel sheet in an amount of 0.1% or more, good appearance properties and plating adhesion can be ensured. A preferable Si amount is 0.5% or more, more preferably 0.8% or more. However, if Si is added excessively, ductility deteriorates, so the content is made 3.0% or less. A preferable amount of Si is 2.5% or less, more preferably 2.0% or less.

Mn: 0.1 to 3.0%
Mn is an element necessary for securing strength and toughness, and is contained in an amount of 0.1% or more in order to effectively exhibit such action. According to the present invention, the oxidation heating conditions in the heating furnace are appropriately controlled as will be described later. Therefore, even if 0.1% or more of Mn is added, it is possible to avoid a decrease in plating adhesion. A preferable amount of Mn is 0.2% or more, more preferably 0.5% or more. However, if Mn is added excessively, ductility deteriorates, so the content is made 3.0% or less. A preferable amount of Mn is 2.5% or less, and more preferably 2.3% or less.

  The base steel sheet used in the present invention contains the above elements as basic elements, and the balance is iron and inevitable impurities. Among inevitable impurities, for example, P is 0.02% or less (0% is not included), S is 0.004% or less (0% is not included), and N is 0.01% or less (0% is not included). It is preferable that

P: 0.02% or less (excluding 0%)
P has an effect of suppressing the transformation by delaying the precipitation of cementite, but if contained excessively, it causes a decrease in the ductility and plating adhesion of the base steel sheet. Therefore, P is 0.02% or less, preferably 0.01% or less, more preferably 0.005% or less.

S: 0.004% or less (excluding 0%)
When S is excessively contained, a large amount of sulfide inclusions (for example, MnS) such as MnS are formed, and these inclusions segregate during hot rolling and cause embrittlement of the steel sheet. Therefore, S is 0.004% or less, preferably S 0.003% or less, more preferably 0.002% or less.

N: 0.01% or less (excluding 0%)
When N is excessively contained, a large amount of coarse nitride is formed, which deteriorates the bendability and hole expandability of the steel sheet, and causes blowholes during welding. Therefore, N is 0.01% or less, preferably 0.005% or less, more preferably 0.002% or less.

  The base steel sheet used in the present invention can further contain the following elements as other elements as required.

  Ni, Cu, Mo, and B are elements useful for improving the hardenability, and these elements can be used alone or in combination. Specifically, it is as follows.

Ni: 2% or less (excluding 0%)
Ni is an element useful for improving hardenability. When an appropriate amount of Ni is added, the martensite ratio increases during CAL annealing and cooling, the lath structure of martensite is refined, and the hardenability during the two-phase reheating / cooling process during CGL annealing in the next process is good. It becomes. Moreover, since the final composite structure after cooling becomes favorable, various molding processability can be improved. In order to effectively exhibit such an action, Ni is preferably contained in an amount of 0.1% or more, more preferably 0.2% or more. However, Ni is an expensive element, and if it is added excessively, the manufacturing cost increases, so it is preferably made 2% or less. A more preferable amount of Ni is 1.5% or less, and further preferably 1.0% or less.

Cu: 2% or less (excluding 0%)
Cu, like Ni, is an element useful for improving hardenability. Cu can improve various processability by the same action as Ni. In order to effectively exhibit such an action, Cu is preferably contained in an amount of 0.1% or more, more preferably 0.2% or more. However, Cu is an expensive element, and if added excessively, the manufacturing cost is increased, so the content is preferably 2% or less. A more preferable amount of Cu is 1.5% or less, still more preferably 1.0% or less.

Mo: 2% or less (excluding 0%)
Mo is an important element in strengthening the solid solution without impairing the plating property. Moreover, like Ni and Cu, it is an element useful for improving hardenability. Mo can improve various moldability by the same action as Cu and Ni. In order to effectively exhibit such an action, Mo is preferably contained in an amount of 0.1% or more, more preferably 0.2% or more. However, Mo is an expensive element, and if added excessively, the manufacturing cost is increased, so the content is preferably 2% or less. A more preferable amount of Mo is 1.5% or less, and further preferably 1.0% or less.

B: 0.01% or less (excluding 0%)
B is an element useful for improving hardenability. In order to effectively exhibit such an action, B is preferably contained in an amount of 0.0001% or more, more preferably 0.0002% or more. However, if B is added excessively, the plating property is lowered, so the content is preferably 0.01% or less. A more preferable amount of B is 0.005% or less, still more preferably 0.001% or less.

  Cr, Nb, V, and W are elements useful for improving the strength, and these elements can be used alone or in combination. Specifically, it is as follows.

Cr: 2% or less (excluding 0%)
Cr is an element effective for improving the strength of the steel sheet. In order to effectively exhibit such an action, Cr is preferably contained in an amount of 0.01% or more, more preferably 0.05% or more. However, excessive addition of Cr causes a drop in ductility, so it is preferably 2% or less, more preferably 1.5% or less, and even more preferably 1.0% or less.

Nb: 1% or less (excluding 0%)
Nb is an element useful for increasing the strength without degrading toughness because a fine structure can be obtained with a small amount of addition. In order to effectively exhibit such an action, Nb is preferably contained in an amount of 0.001% or more, more preferably 0.005% or more. However, when Nb is added excessively, Nb carbides are excessively generated, which causes a loss of the balance between strength and workability due to a decrease in the martensite volume fraction and precipitation strengthening. Therefore, Nb is preferably 1% or less, more preferably 0.5% or less, and still more preferably 0.1% or less.

V: 1% or less (excluding 0%)
V, like Nb, is an element useful for increasing the strength. In order to effectively exhibit such an action, V is preferably contained in an amount of 0.001% or more, more preferably 0.005% or more. However, when V is excessively added, not only the manufacturing cost is increased, but also the yield point (yield ratio) is increased and the workability is decreased. Therefore, V is preferably 1% or less, more preferably 0.5% or less, and still more preferably 0.1% or less.

W: 0.3% or less (excluding 0%)
W is an element useful for increasing the strength by strengthening precipitates, strengthening fine grains by suppressing the growth of ferrite crystal grains, and transition strengthening by suppressing recrystallization. In order to effectively exhibit such an action, W is preferably 0.001% or more, more preferably 0.005% or more. However, if W is added excessively, the precipitation of carbonitrides becomes excessive, which causes a decrease in moldability. Therefore, W is preferably 0.3% or less, more preferably 0.2% or less, and still more preferably 0.1% or less.

  Al and Ti are elements useful as deoxidizers. Specifically, it is as follows.

Al: 0.06% or less (excluding 0%)
Al is an element that acts as a deoxidizer. In addition, Al is an element that prevents the austenite crystal grains from coarsening during annealing and has a material improving effect. However, even if Al is added excessively, the above action is saturated. In addition, the crystal grains become unstable and unevenness is likely to occur in the material. Therefore, Al is preferably 0.06% or less, more preferably 0.05% or less, and still more preferably 0.04% or less.

Ti 0.1% or less (excluding 0%)
Ti is an element that acts as a deoxidizer. In order to effectively exhibit such an action, Ti is preferably 0.01% or more, more preferably 0.02% or more. However, excessive addition of Ti causes a reduction in toughness. Therefore, Ti is preferably 0.1% or less, more preferably 0.008% or less, and more preferably 0.005% or less.

At least one element selected from the group consisting of Ca, Mg, and REM: 0.03% or less in total (not including 0%)
Ca, Mg, and REM are elements that act as deoxidizers. These elements can be used alone or in combination. In order to effectively exert such an action, the total amount of one or more elements selected from the group consisting of Ca, Mg, and REM is preferably 0.002% or more, more preferably 0.003% or more. To do. However, when these elements are added excessively, the moldability is lowered. Therefore, the total amount of one or more elements selected from the group consisting of Ca, Mg, and REM is preferably 0.03% or less, more preferably 0.02% or less, and still more preferably 0.01% or less.

  In the present invention, REM means a lanthanoid element (15 elements from La to Lu), Sc (scandium) and Y (yttrium). Among these elements, it is preferable to contain at least one element selected from the group consisting of La, Ce and Y, more preferably La and / or Ce.

  An alloyed hot-dip galvanized steel sheet can be manufactured by going through the first to third steps using a base steel plate that satisfies the above component composition, but in particular, the first step (characterizing the manufacturing method of the present invention most particularly ( The conditions for performing the oxidation step are as follows.

First step (oxidation step)
The first step defines an oxidation step for forming an oxide layer on the surface of the base steel plate. At this time, (a) the amount of oxygen in the heating furnace is 0.3% by volume or less, and the amount of water vapor is 10-30. Under an atmosphere controlled to volume%,
(B) heating the base steel plate to a temperature of 750 to 850 ° C. in 45 to 120 seconds;
(C) While heating to 450-600 degreeC with the temperature increase rate (X) of 7.5-28 degreeC / second (heating pre-stage process),
(D) After that, it is important to further heat to a temperature of 750 to 850 ° C. at a heating rate (° C./second) of 0.30X to 0.80X (post-heating step).

[(A) Atmosphere in heating furnace]
Oxygen amount: 0.3 volume% or less As described above, if the oxygen amount is excessively increased, the inner oxide layer becomes too thick and the amount of Si contained in the inner oxide layer becomes excessive. appear. Therefore, the amount of oxygen is set to 0.3% by volume or less. A preferable oxygen amount is 0.2% by volume or less, more preferably 0.15% by volume or less. On the other hand, in order to improve the appearance properties, the oxygen content is preferably 0.00001% by volume or more. If the amount of oxygen is small, the outer oxide layer is not sufficiently formed, and the Fe layer (reduced layer) formed by reducing the outer oxide layer in the reducing furnace becomes thin, which causes problems such as non-plating. A preferable oxygen amount is 0.001% by volume or more, more preferably 0.01% by volume or more.

Water vapor amount: 10-30% by volume
The water vapor has an action of promoting the growth of both the outer oxide layer and the inner oxide layer. When the amount of water vapor is less than 10% by volume, the thickness of the outer oxide layer is insufficient, so that non-plating and poor alloying occur and appearance properties deteriorate. The amount of water vapor is 10% by volume or more, preferably 15% by volume or more. However, when the amount of water vapor is excessive, the growth of the outer oxide layer is promoted too much and the growth of the inner oxide layer is also promoted, so that the amount of Si contained in the plating layer increases and plating peeling at the interface occurs. Therefore, the amount of water vapor is 30% by volume or less, preferably 25% by volume or less.

  The amount of oxygen and water vapor contained in the atmosphere in the heating furnace can be adjusted by adjusting the flow rate of the combustion gas supplied to the burner used when heating the heating furnace and the flow rate ratio (air-fuel ratio) of the combustion gas and air. Can be controlled. The amount of oxygen in the heating furnace can be measured using, for example, a magnetic densitometer, and the amount of water vapor can be measured using, for example, a dew point meter.

[(B) Heating time in heating furnace]
Heating time: 45 to 120 seconds The base steel sheet is heated to 750 to 850 ° C in 45 to 120 seconds. In the case of a direct-fired heating furnace, if the heating time is short, the oxidation process must be completed within a short time, increasing the burden on the equipment and increasing the maintenance cost. If the heating time is short, desired material characteristics cannot be obtained. Accordingly, the heating time is 45 seconds or longer. A preferable heating time is 55 seconds or more. On the other hand, productivity decreases as the heating time increases. In addition, the inner oxide layer becomes too thick and the amount of Si contained in the inner oxide layer increases, resulting in peeling of the plating at the interface. Therefore, the heating time is 120 seconds or less. A preferred heating time is 110 seconds or less. This heating time is the time when the furnace inlet temperature, that is, the temperature of the base steel plate starts from room temperature. Therefore, when making the temperature of a base steel plate higher than room temperature, what is necessary is just to adjust a heating time suitably in connection with it.

[(C) Pre-heating step]
Heat to 450 to 600 ° C. at a temperature rising rate (X) of 7.5 to 28 ° C./sec. Temperature before heating: 450 to 600 ° C.
In the present invention, the range from the heating furnace inlet to 450 to 600 ° C. is the pre-heating step, and the temperature increase rate in the pre-heating step is 7.5 to 28 ° C./second. The furnace inlet temperature is preferably room temperature, but is not limited thereto. 450-600 degreeC is made into the completion | finish temperature of a pre-heating stage, and it transfers to a post-heating post process after that. When the process proceeds to a post-heating step at a temperature lower than 450 ° C., the processing time in the low temperature range is eliminated, so that an oxide layer mainly composed of hematite is generated, and as described above, adhesion between the base steel sheet and the inner oxide layer The sex cannot be raised sufficiently. Therefore, the end temperature of the pre-heating stage is 450 ° C. or higher. A more preferable end temperature of the pre-heating stage is 470 ° C. or higher. On the other hand, when the end temperature of the former stage exceeds 600 ° C., the in-furnace time in the high temperature region (post-heating stage process) is shortened due to the restriction of the rate of temperature rise in the latter stage, which causes alloying failure. Therefore, the end temperature of the pre-heating step is 600 ° C. or lower. A more preferable end temperature of the pre-heating step is 580 ° C. or lower.

Heating rate of pre-heating step: 7.5 to 28 ° C./second In the present invention, heating is performed to a temperature of 450 to 600 ° C. at a temperature rising rate of 7.5 to 28 ° C./second. If the heating rate in the pre-heating stage is too slow, not only the productivity is lowered, but also the hematite-based oxide generated in the low temperature region increases, which causes the occurrence of plating adhesion as described above. Therefore, the heating rate in the pre-heating stage is 7.5 ° C./second or more, preferably 10 ° C./second or more. On the other hand, if the heating rate of the pre-heating stage is too high, the pre-heating stage must be completed quickly, increasing the burden on the equipment. If the heating time is short, desired material characteristics cannot be obtained. Therefore, the heating rate in the pre-heating stage is 28 ° C./second or less, preferably 25.5 ° C./second or less.

[(D) Post-heating step]
Further heating to 750 to 850 ° C. at a temperature rising rate (° C./second) of 0.30X to 0.80X In the present invention, the range from the heating pre-stage process end temperature to 750 to 850 ° C. is defined as the heating post-stage process. The rate of temperature increase in the subsequent step is 0.30X to 0.80X [X is the rate of temperature increase in the pre-heating step (° C./second)].

  If the end temperature of the post-heating step is too low, the diffusion of Fe contained in the base steel plate is not sufficient, resulting in insufficient thickness of the outer oxide layer, resulting in poor alloying and the like, causing deterioration in appearance properties. Therefore, the end temperature of the post-heating step is 750 ° C. or higher. The preferred end temperature is 770 ° C. or higher. On the other hand, if the end temperature of the post-heating step becomes too high, Si contained in the base steel sheet is excessively concentrated in the inner oxide layer, which causes a decrease in adhesion between the base steel sheet and the plating layer. Therefore, the end temperature of the latter stage of heating is set to 850 ° C. or lower. The preferred end temperature is 840 ° C. or lower.

Temperature increase rate in the latter heating process: 0.30X to 0.80X [X is the temperature increase speed in the heating earlier process (° C./second)]
As described above, the outer oxide layer is formed by diffusion of Fe inside the base steel sheet to the surface side, and this diffused Fe is oxidized, so when the high temperature region stay time of the base steel sheet becomes too long, The diffusion of Fe is promoted excessively and the outer oxide layer becomes too thick. As a result, in the reduction treatment step to be described later, the pure Fe layer formed by the reduction of the outer oxide layer becomes too thick, so that when the hot dip galvanizing treatment is performed, the amount of reduced iron that reacts with zinc increases and the zinc adheres. It becomes the cause which becomes overdose. Moreover, since the oxidation of Si diffused on the surface of the base steel sheet increases and the thickness of the inner oxide layer also increases, this causes the plating to peel from the interface as described above. Therefore, the temperature raising rate is set to 0.30X or more. A preferable temperature increase rate is 0.35X or more. On the other hand, if the rate of temperature rise is too high, the oxidation of Si diffused on the surface of the base steel sheet is not sufficient, and the adhesion between the base steel sheet and the inner oxide layer is reduced due to insufficient generation of firelight, and the plating peeling at the interface Will occur. Therefore, as shown in FIG. 1 (d), molten zinc penetrates into the gaps formed by the peeling during immersion in the hot dip galvanizing bath, resulting in excessive zinc adhesion. Further, since the diffusion of Fe is not sufficient, the outer oxide layer becomes thin. As a result, in the reduction process, the thickness of the reduced layer formed by the reduction of the outer oxide layer is reduced, so that non-plating and poor alloying occur, resulting in poor appearance properties. Further, the amount of Si oxide observed on the exposed surface after immersion in an aqueous ammonia solution and removal of the alloyed hot-dip galvanized layer is reduced. As a result, the occurrence of poor alloying is further promoted. Therefore, the rate of temperature rise is 0.80X (° C / s) or less. A more preferable temperature increase rate is 0.75X or less.

  The boundary between the pre-heating step and the post-heating step can measure the heat pattern of the temperature of the base steel sheet, and the pre-heating step and the post-heating step can be separated at the position of the maximum inflection point in the heat pattern.

  Moreover, if the temperature increase rate of a pre-heating process and a post-heating process is in the said range, it may be a fixed temperature increase rate, and may change a temperature increase rate on the way.

  The heating equipment for performing the first step is not particularly limited. For example, the above process is performed as a pre-heating step from the heating furnace inlet to the intermediate position of the heating furnace, and then from the intermediate position of the heating furnace to the heating furnace outlet. You may perform the said process as a heating furnace back | latter stage process. In this case, it is desirable to control so that the heating time is the same in the heating furnace pre-stage process and the heating furnace post-stage process, and the above processing is performed within the heating time. Of course, depending on the configuration of the heating furnace, it is not always necessary to separate the pre-heating stage and the post-heating stage at an intermediate position of the heating furnace, and the treatment at the predetermined temperature range and the heating rate may be the pre-heating process and the post-heating process. In this case, the heating time of the heating furnace pre-stage process and the heating furnace post-stage process may be the same or may be changed.

  In addition, the temperature of the said pre-heating process and post-heating process is the temperature of a steel plate, specifically, the surface temperature of the steel plate measured with a radiation thermometer.

  The first process characterizing the present invention has been described above.

  After the first step, the second step (reduction treatment step) and the third step (plating / alloying treatment step) are performed. The second step and the third step are alloyed molten zinc. A method usually used when producing a plated steel sheet can be employed.

<< Second process (reduction treatment process) >>
In the second step, the desired pure Fe layer (reduced layer) is formed on the surface of the base steel sheet by reducing the oxidized layer (mainly the outer oxidized layer) formed in the first step with a reducing furnace. To do. At this time, a part of the inner oxide layer is also reduced, and the inner oxide layer becomes a layer in which oxide and Fe are mixed.

The atmosphere in the reduction furnace may be a reducing gas atmosphere. The reducing gas atmosphere is, for example, an H ₂ gas-containing N ₂ gas atmosphere. The temperature in the reduction furnace may be about 800 to 950 ° C., and the reduction time may be about 30 seconds to 3 minutes.

«Third step (plating / alloying step)»
In the third step, the surface of the pure Fe layer is hot dip galvanized and then alloyed to form an alloyed hot dip galvanized layer. At this time, Fe contained in the layer in which the oxide and Fe are mixed is also alloyed with Zn to form an oxide-containing layer in which the Zn—Fe alloy and Si—Mn oxide are mixed.

The conditions for hot dip galvanizing and the conditions for alloying are not particularly limited, and known conditions can be adopted. The temperature of the hot dip galvanizing bath may be about 400 to 600 ° C. The alloying temperature may be about 500 to 600 ° C. Adhesion amount of the galvannealed layer may be a 30~70g / m ² approximately.

  The plated steel sheet of the present invention can be manufactured by performing a base steel sheet satisfying the above component composition from the first process to the third process (oxidation process → reduction process → plating / alloying process). .

  The plated steel sheet thus obtained has improved plating adhesion, appearance, and plating adhesion.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. All of these are possible within the scope of the present invention.

  First, steels A to W containing the chemical components shown in Table 1 (the balance is inevitable impurities other than iron and P, S, and N) were melted to produce slabs. The obtained slab was heated to 1200 ° C. and hot-rolled to obtain a hot-rolled steel sheet. The obtained hot-rolled steel plate was pickled to remove the scale, and was cold-rolled to produce a thin steel plate (base steel plate) having a thickness of 2.0 mm.

  Next, the obtained steel sheet is pickled to remove scales, heated in a heating furnace under the conditions shown in Table 2 to form an oxide layer, and after reducing this oxide layer in a reduction furnace, hot dip galvanizing After entering the bath, wiping was performed to obtain a hot dip galvanized steel sheet. Thereafter, alloying treatment was further performed in an alloying furnace to obtain an alloyed hot-dip galvanized steel sheet.

  Specific conditions in the heating furnace and the reduction furnace are as follows. The surface temperature of the thin steel plate was measured using a radiation thermometer, the oxygen content was measured using a magnetic densitometer, and the water vapor content was measured using a dew point meter.

In the heating furnace, the thin steel plate was heated by burning a mixed gas of combustion gas and air with a burner. As the combustion gas, COG gas is used. This COG gas contains 55% by volume of H ₂ gas and 6% by volume of N ₂ gas, and the remainder is composed of hydrocarbon gas. The partial pressure of oxygen contained in the atmosphere gas in the heating furnace was 0.1% by volume, and the partial pressure of water vapor was 20% by volume. Other heating conditions (heating time, temperature increase rate, end temperature) are as shown in Table 2.

  In the pre-heating step, heating was performed such that the heating start temperature in the post-heating step became the temperature shown in Table 2 below (end temperature of the pre-heating step). The heating conditions in the pre-heating step were controlled by adjusting the temperature in the heating furnace and the plate passing speed. The heating furnace inlet temperature was room temperature (20 ° C.).

  In the post-heating step, the thin steel plate was heated to form an oxide layer on the surface of the thin steel plate, as in the pre-heating step. Moreover, it heated so that the heating completion temperature in a post-heating process may turn into the temperature shown in Table 2 below. The heating conditions in the post-heating step were controlled by adjusting the temperature in the heating furnace and the plate passing speed.

Next, the said thin steel plate was supplied to the reduction furnace, and the oxide layer was reduced. Here, the reduction furnace provided with the radiant tube was used, and it heated so that the steel plate temperature in a reduction furnace exit might be set to 950 degreeC by the method of raising the temperature of the said thin steel plate indirectly. The atmosphere in the reduction furnace was an N ₂ gas atmosphere containing 20% by volume of H ₂ .

Next, the steel sheet is cooled while maintaining the reducing atmosphere, and the steel sheet is immersed in a hot dip galvanizing bath (450 ° C.) without contacting with the air. It took out and compressed air was sprayed perpendicularly | vertically with respect to the thin steel plate surface from the wiping nozzle. In the wiping, the interval between the wiping nozzle and the thin steel plate and the nozzle air pressure were appropriately adjusted so that the coating amount of the thin steel plate measured online was 40 g / m ² .

  After hot dip galvanization, it was further heated at 500 ° C. in an alloying furnace for alloying treatment to produce an alloyed hot dip galvanized steel sheet.

  About each obtained galvannealed steel plate, the adhesiveness of plating, plating adhesiveness, and external appearance property were evaluated in the following procedure.

(Plating adhesion)
If the amount of zinc adhering to the base steel sheet cannot be controlled properly when hot dip galvanizing is performed, peeling between the base steel sheet and the oxide layer has occurred, and hot dip galvanization has entered the gaps formed at the peeling locations. Since the plating adhesion described above is caused by the subsequent alloying treatment, the following test method was adopted as a method for predicting the occurrence of plating adhesion.

Evaluation was made based on whether or not the amount of plating adhesion after the hot dip galvanizing on the thin steel sheet could be properly controlled. Specifically, the amount of plating adhered after hot dip galvanization is measured using fluorescent X-rays, and the interval between the wiping nozzle and the thin steel plate and the air pressure sprayed from the nozzle are varied based on the measured values obtained. The process which controls the plating adhesion amount to 40 g / m ² was performed. After the treatment, the amount of plating adhesion was measured again using fluorescent X-rays. In the present Example, what was able to control the plating adhesion amount to 40 +/- 10g / m < ² > was evaluated as the pass ((circle)).

(Evaluation of plating adhesion)
The plated steel sheet was processed into a plate-shaped specimen having a length of 100 mm, a width of 200 mm, and a thickness of 2 mm, and a V-bending / returning test was performed to evaluate the plating adhesion. This V-bending / bending test simulates conditions more severe than actual press forming. When the tape peeling width is 5 mm or less, the plating layer can be peeled off even in actual pressing (bending angle 90 °). It has been confirmed that it does not occur. Specifically, the test piece was subjected to V-bending using a V-bending test die (bending angle of 60 °), and then bent back to return the test piece to a flat shape with a press. A cellophane tape (“Cello Tape (registered trademark) CT405AP-24” manufactured by Nichiban Co., Ltd.) is applied to the inner surface (deformed portion) when the bending back process is performed, and the plating layer adhered to the tape is peeled off by hand. The peel width was measured. In this example, a strip width of 5 mm or less was evaluated as acceptable (excellent in plating adhesion) (units in the table are all mm).

  In addition, as a result of investigating all the examples in which plating peeled in the examples, the cause of plating peeling was that the plating layer was peeled from the thin steel plate (plating peeling at the interface).

(Appearance properties)
Appearance properties were determined by visually observing the appearance of the alloyed hot-dip galvanized layer, and checking for alloying defects and non-plating. In this example, a case where neither alloying failure nor non-plating occurred was evaluated as pass (◯), and a case where non-plating and / or alloying failure occurred was determined as failure (x). .

  The test results are shown in Table 3.

  From Table 3, it can be considered as follows.

  First, no. 1-3 are examples in which the end temperature of the post-heating step is changed. Of these, No. No. 1 is an example in which the end temperature of the post-heating step is low, and the thickness of the outer oxide layer is insufficient, resulting in poor alloying and non-plating, resulting in poor appearance properties. No. No. 2 is an example that satisfies the requirements defined in the present invention, and can prevent the occurrence of alloying failure and non-plating and has good appearance properties. In addition, plating adhesion and zinc content can be improved. No. No. 3 is an example in which the end temperature of the post-heating step is high, Si is excessively concentrated, a large amount of Si oxide is generated, and plating adhesion is deteriorated.

  Next, no. Examples 4 to 7 and 37 to 40 are examples in which the end temperature of the pre-heating step is changed. Of these, No. Nos. 4 and 37 are examples in which the end temperature of the pre-heating step is low, and hematite is generated on the surface of the base steel plate. As a result, the amount of plating is large and the adhesion of plating is deteriorated.

  No. Nos. 5, 6, 38 and 39 are examples satisfying the requirements defined in the present invention, and it is possible to prevent the occurrence of alloying defects and non-plating and have good appearance properties. In addition, plating adhesion and zinc content can be improved. No. Nos. 7 and 40 are examples in which the end temperature of the pre-heating step is high. Since the end temperature of the pre-heating step exceeds 600 ° C., the rate of temperature increase in the post-heating step is restricted and there is a high temperature region (post-heating step). Furnace time is shortened, poor alloying occurs, and appearance properties are degraded.

  Next, no. Nos. 8 to 12 and 32 to 36 are examples in which the heating rate of the post-heating step is changed with respect to the heating rate (X) of the pre-heating step. Of these, No. 8 and 32 are examples in which the heating rate of the heating post-stage heating is lower than 0.30X with respect to the heating speed of the heating pre-stage process, and the residence time in the post-heating stage process becomes too long and the outer oxide layer becomes too thick. Therefore, the pure Fe layer formed by the reduction treatment is too thick, the amount of reduced iron that reacts in the hot dip galvanizing bath is increased, the amount of hot dip galvanizing is increased, and the adhesion of the plating is deteriorated. In addition, the thickness of the inner oxide layer increases, and as a result, the adhesion of the plating is poor and the plating adhesion is also deteriorated.

  No. Reference numerals 9 to 11 and 33 to 35 are examples satisfying the requirements defined in the present invention, and the plating adhesion, plating adhesion, and appearance are good.

  No. Nos. 12 and 36 are examples in which the heating rate of the post-heating step exceeds 0.80X with respect to the heating rate (X) of the pre-heating step, and since the formation of firelight is insufficient, the adhesion of the plating deteriorates. At the same time, the thickness of the outer oxide layer is insufficient, resulting in poor alloying and non-plating, resulting in poor appearance.

  Next, no. 13 to 31 are examples using steel plates having various steel components. No. Nos. 13 to 31 are examples satisfying the requirements defined in the present invention, and are good in plating adhesion, plating adhesion, and appearance properties.

Claims (5)

C: 0.04 to 0.20% (meaning mass%. The same applies to chemical components below),
Si: 0.1 to 3.0%,
Mn: 0.1 to 3.0%
A method for producing an alloyed hot-dip galvanized steel sheet in which an alloyed hot-dip galvanized layer is formed on the surface of the base steel sheet satisfying
A first step of forming an oxide layer on the surface of the base steel sheet by heating the base steel sheet satisfying the chemical component composition in a heating furnace;
A second step of heating the base steel sheet on which the oxide layer is formed in a reduction furnace to reduce the oxide layer;
A third step of alloying after galvanizing, in this order,
In the first step, the base steel plate is placed in a range of 750 to 850 in 45 to 120 seconds in an atmosphere in which the oxygen amount in the heating furnace is controlled to 0.3% by volume or less and the amount of water vapor is controlled to 10 to 30% by volume. Heating to a temperature of 0 ° C., and
The first step is a pre-heating step for heating to a temperature of 450 to 600 ° C. at a temperature rising rate (X) of 7.5 to 28 ° C./second,
And a heating post-stage step of further heating to a temperature of 750 to 850 ° C. at a temperature rising rate of 0.30X to 0.80X.   The base steel sheet further includes Ni: 2% or less (not including 0%), Cu: 2% or less (not including 0%), Mo: 2% or less (not including 0%), and B: 0.0. The manufacturing method of the plated steel plate of Claim 1 containing at least 1 sort (s) selected from the group which consists of 01% or less (0% is not included).   The base steel sheet further includes Cr: 2% or less (not including 0%), Nb: 1% or less (not including 0%), V: 1% or less (not including 0%), and W: 0.0. The manufacturing method of the plated steel plate of Claim 1 or 2 containing at least 1 sort (s) selected from the group which consists of 3% or less (0% is not included).   The base steel sheet further contains Al: 0.06% or less (not including 0%) and / or Ti: 0.1% or less (not including 0%). The manufacturing method of the plated steel plate of description.   The base steel sheet further contains at least one element selected from the group consisting of Ca, Mg, and REM: 0.03% or less (excluding 0%) in a total amount. The manufacturing method of the plated steel plate as described in any one of.